Load Image -> CopyStructure(), GetArray() and AddArray() -> 'Save Data...' cannot work??

1. Load some image data. (*.png etc.)
2. Apply Programmable Filter.
3. Apply 'Save Data...' to the Programmable Filter, but no data is saved with some warning.

The setting of the Programmable Filter is as follows:

# Output Data Set Type: Same as Input
# Script:
pdi = self.GetInput()
pdo = self.GetOutput()

pdo.CopyStructure(pdi)
pdo.GetPointData().AddArray(pdi.GetPointData().GetArray('PNGImage'))

And the warning is as follows:

Warning: In /Users/kitware/buildbot-slave/b99e1795/source-paraview/VTK/IO/Image/vtkPNGWriter.cxx, line 231
vtkPNGWriter (0x6000005a8260): PNGWriter only supports unsigned char and unsigned short inputs

This is just a tiny example. The actual codes are heavily complicated, but they also have the same issue.

This issue happens PV 5.2.0 or older version.